Dec 18 (Reuters) - The U.S. Food and Drug Administration

on Wednesday classified a recall of Boston Scientific's ( BSX )

catheters used in a type of minimally invasive surgery as "most

serious".

The recall involves updating instructions for use rather

than removing the device, POLARx Cryoablation Balloon Catheters,

from where they are used or sold, the FDA said.

The company meanwhile is revising the use instructions of

the catheter due to a higher-than-anticipated number of reports

of esophageal injury, specifically a complication known as

atrio-esophageal fistula, which can lead to air bubbles blocking

blood vessels in the brain.

The FDA said the use of the affected products may also cause

stomach and intestinal bleeding, a system-wide infection, and

even death.

There have been seven reported injuries and four deaths, the

health regulator added.

On Oct. 10, Boston Scientific ( BSX ) sent an urgent medical device

advisory to all affected customers with recommendations.

Boston's device is used in ablation procedures to treat

recurrent symptomatic atrial fibrillation that causes irregular,

fast heartbeats lasting up to seven days and not responding to

medication.

Ablation is a minimally invasive procedure used to treat

atrial fibrillation by creating scars on the heart tissue.